Occasionally, when accelerating, the car has a pronounced jerk. At first I thought it was a clutch slip, but it only happens when I have my foot down on the accelerator and the clutch is fully up. Only happens in 4th, 5th or 6th gear, when accelerating reasonably firmly. I had a new clutch & DMF done about 15k back (car has 114k on it), and the car is totally fine on any clutch test. So if itís not the clutch, thinking it something with air of fuel? I get the odd bit of smoke, but the car is in excellent nick (FSH, regularly serviced, new oil and filters (including DPF)

I have recently started using some diesel additive (Redex Fuel System cleaner) Ė have been putting in for the last 2 tanks Ė but definitely adding the right amount. Wondering if itís dislodging some carbon build up somewhere, or if there could be some valve thatís got clogged by released crud? Car was put on diagnostic too, and nothing came up.

Any ideas what might be causing this, or how I might go about diagnosing?